The term "drying and ironing machine with a trough" is to be understood as meaning a machine in which a flat piece of fabric, still damp (generally after completion of the wash and spin dry cycle of a washing machine) and drawn by a rotating cylinder, is dried and ironed by friction against the polished inner surface of a heated trough, generally of semi-cylindrical shape, against which the rotating cylinder applies it. By analogy with domestic ironing, one may say that in this machine it is the fixed trough which plays the part of the flat-iron while the rotating cylinder plays the part of the ironing table.
The heated trough rises to a temperature of about 200.degree. C. by such means as the circulation of pressured steam and heats, by contact, the damp piece of fabric and dries it by vaporization of the residual water impregnating it, while ironing it by friction on this surface.
The cylinder is perforated over its whole cylindrical surface by a large number of openings and this cylindrical surface is completely wrapped by a sleeve-like elastic and permeable outer lining substituting for the table felt used in domestic ironing. This elastic lining ensures the uniform application of the piece of fabric against the polished inner surface of the trough as the piece of fabric travels along the trough.
The steam resulting from the vaporization of the residual water impregnating the piece of fabric passes through this outer lining and penetrates into the inside of the cylinder through its openings from where it is evacuated by suction.
It can easily be understood that the quality of the ironing depends upon the uniformity of the pressure of application of the piece of fabric along its whole length against the surface of the trough. Now, this uniformity is only achievable if the cylinder and the polished inner surface of the heated trough remain coaxial at ironing temperature. Both being coaxial in the cold state and the polished inner surface of the heated trough remaining applied to the cylinder through the piece of fabric pressed against the cylinder outer lining, this cylinder and the said polished surface can no longer be coaxial at ironing temperature due to their different rates of expansion, as follows:
the cylinder and the trough have heat expansion coefficients which are similar or equal since both are made of rolled boiler-type steel sheet metal. But, while the entire polished inner surface of the trough remains permanently heated to about 200.degree. C., only a portion of the cylinder is exposed, at the time, to this heated surface of the trough through the cylinder outer lining, thus making the trough much warmer and expanded than the cylinder during full operation of the drying and ironing machine;
while the cylinder is a closed surface, the inner surface of the trough is an opened one which features exposed edges and which, since it is made by the bending of boiler-type steel sheet metal which creates permanent stress within the metal, is therefore subject to internal temperature variations which results, at any given heating temperature, in a greater increase of its radius of curvature than if it was carved out of homogeneous steel block free of internal stress, a circumstance which does not apply to the cylinder even though it is also made of bent boiler-type steel sheet metal, owing to continuous nature of its surface;
the preferred use of pressured steam, as a means to heat the trough, itself tends to increase the radius of curvature of the (heating) polished inner surface of the trough, due to the pressure created by the steam upon such surface.
It follows that, during the operation mode of the machine, the curvature of the heating polished inner surface of the trough is substantially less than that of the cylinder with its outer lining and that this inner (concave) surface of the trough progressively separates itself from the face of the cylinder as it nears the horizontal diameter of the cylinder where it creates a gap ("e" in FIG. 3) which is obviously proportional, in size, to the diameter of the cylinder of the machine.
In appliances with small cylinder diameter, the resilience alone of the cylinder outer lining, while not achieving the uniformity of pressure aimed as above, is sufficient, however, to keep this pressure substantially uniform along the inner surface of the trough.
In appliances with larger cylinder diameter (i.e. some tens of centimeters) one has recourse to the following expedient: between the cylinder and its outer lining is placed a large number of small springs acting radially and which keep, via the cylinder outer lining, the piece of fabric pressed against the heated inner (concave) surface of the trough, these radial springs becoming increasingly compressed the more they approach the lower part of the said inner surface of the trough. This solution, however, has the drawback of subjecting the cylinder outer lining to variable stresses which accelerate its aging as well as its wear and tear, and to permanently strain the springs which, by being located in a humid environment, can deteriorate in an unpredictable way.
In appliances with still larger cylinder diameter (more than 100 cm) and such as the type referred to in this invention, the above-mentioned expedient, already open to criticism in itself, proves to be unapplicable, since the then oversized gap "e" mentioned above can no longer be compensated by this means.
For machines of this latter type, one could conceive several ways to compensate or eliminate this gap "e".
One could think of sizing, in the cold state, the inner (concave) surface of the trough to a lesser diameter than that of the cylinder with its outer lining and such that, the trough being brought to ironing temperature and expanding thereafter, these diameters come to match each other. However, since this solution would require the maintenance of a well-defined ironing temperature to keep the trough relatively free from the cylinder in the cold state, it would prove to be unfeasible.
One could also try to eliminate the said gap by undersizing the diameter of the inner (concave) surface of the trough relative to that of the cylinder with its lining. However, this would generate substantial lateral forces hindering the rotation of the cylinder to the point of blocking its movement.
Last, one could try to reduce this gap "e" by dividing the surface of the trough into several curved and articulated sectors, hinged lengthwise to one another. For n equal sectors the gap "e" would thus be reduced to "e"/n and therefore be smaller as one increases the number of these equal sectors. However, this solution would have the drawback of producing, at each articulation between two sectors, a discontinuity of the inner (concave) surface of the trough on which the front edge of the piece of fabric would butt against, and jam the machine. In addition, each of the said articulations could corrode, considering the damp environment in which the trough operates. Some of the articulations could then lock in unpredictable positions and disrupt the regularity of the curvature of the inner (concave) surface of the trough.